This invention relates generally to structures supporting optically correct prescription lenses for those who must wear protective masks, and more particularly to a support structure designed to be used with foldable protective masks and to accurately locate and facilitate replacement of prescription or otherwise specialized lenses. This invention may be used by those requiring vision correction and also having to wear protective masks, such as gas masks, full face respirators or welding helmets, scuba goggles, ski goggles, luge helmets and surgical masks, where ordinary spectacles with temples are impractical.
Persons requiring prescription lenses, and using protective face masks must be able to use the presecription lenses at the same time as the face mask. Often, these masks are used in hazardous environments, where it is difficult to see and necessary to be constantly aware of environmental conditions, and the location of emergency exits. Thus, proper adjustment of the prescriptive lenses is crucial.
It is also beneficial to permit changing the lenses for several reasons, as, for instance the persons's prescription changes. Further, in some specialized operations, different colored lenses, or lenses of different composition are required. Thus, easy exchange of the lenses is desired. In the past, several systems have been used to mount prescription or specialized lenses in protective masks. Each of these systems, discussed below, has particular drawbacks.
One method which has been used in the past, secures the lenses in metal frames which are joined by a spring-action nose bridge. A loop of wire or metal is attached to each frame at the location where normally a temple hinge would be found. These loops extend forward of the lenses and toward the center. The protective mask has a bracket near the center of the top of the face plate designed to receive the ends of the loops. Thus, the spectacles are suspended from the inside surface of the mask, by the metal loops. The loops are approximately one and one half times the diameter of each lens.
This metal retaining ring method has several disadvantages. Prescription lenses must be located properly to insure that the lenses will provide the optimum corrective benefit. Several terms must be defined to describe proper fitting of prescription lenses. The "eye-wire" is that part of the frame that encircles and retains an individual lens. The "vertex position" is the vertical position of the lens centers with respect to the pupils. The "pantoscopic angle" is the angle by which the vertical axis of the lens is inclined to a nominal vertical reference with respect to the wearer's face. The "face-form" angle is an angle between two planes. The two planes that defined the face-form angle are the respective planes in which the perimeters of the eyewires lie. With the metal retaining ring structure, the lenses cannot be located accurately in front of the eye to afford optimum visual correction. It is also difficult to maintain the proper pantoscopic angle because of the inherent flexibility of the structure. Thus optimum visual correction is not provided. Similarly, proper face-form angle cannot be maintained due to the spring nose-piece. Vertical adjustment of the lenses is difficult. If the retaining rings are removed from the mask, it is difficult to reposition the lens carrier in the proper vertical position. Finally, lenses cannot be removed from the frame without using special tools, and without removing the lens carrier from the protective mask.
According to a second known method, a lens carrier support anchor is cemented to the inside surface of the face plate, or to the structure which supports the face plate. The anchor piece is designed to receive a semi-flexible tab-like member which is integral with the nose bridge of a spectacle frame. The frame has no temples. Disadvantages of this system are that the relatively flexible tab does not secure the spectacle frames in a secure position, so that the pantoscopic angle can not be fixed. Further, the face-form angle is not easily customizable. Further, it is not possible to fix the vertical adjustment, or the horizontal distance from the pupils to the lenses. Finally, a face mask that may be folded flat when not in use, may not be folded flat when this type of a lens carrier is used.
In another variation, rather than cementing the support anchor to the face plate, the support anchor attaches to the face plate with a suction cup. In addition to the drawbacks mentioned above, this device may be used only for brief periods of time, and is not recommended for dangerous situations because the suction cup may disengage at any time.
Thus, the several objects of our invention include providing a support structure for protective face mask optcial inserts by which: accurate, stable positioning of the optical insert may be obtained; the optical insert may be removed from one mask and easily positioned and attached to another mask; proper pantoscopic and face-form angles may be achieved; proper vertical placement and pupil to lens distances may be achieved; the lenses may be easily removed and replaced without removing the support structure from the mask; the mask and lens support structure may be folded flat while not in use and safe, reliable positioning of the optical inserts may be accomplished.